Add CLI eject command

[arctic-hen7]

Perseus' CLI is to Perseus as create-react-app is to React, but there are cases in which it is too restrictive. These should be few and far between, but, occasionally, it may be required to eject from the CLI and work with the engine of Perseus. To this end, the CLI should support an eject command that removes .perseus/ from the user's .gitignore and gives a brief summary of the powers the user now has.

For those unfamiliar with it, the CLI contains a directory of sub-crates that perform Perseus' internal logic, calling on the perseus and perseus-actix-web crates, as well as the plethora of functions generated by the define_app! macro. Thus, it should be fine to simply expose all this directly to the user, and it's all commented, so it should be reasonably intuitive (after it's been copiously documented).

Note also that the .perseus/ directory has its own .gitignore that ignores the dist/ directory, so the eject command would literally just have to remove .perseus/ from the user's .gitignore. That should be achievable with simple string manipulation, and niche cases can fall back to an error message asking the user to remove the line manually.